1. Field of the Invention
The present invention relates to holography. In particular, the present invention is directed to a method and apparatus for bulk erasure in a holographic storage system.
2. Description of the Related Technology
Holographic techniques for storing images are well known. Such techniques are commonly used to store images in a variety of different applications. Holographic memory is a prospective technology for massive data storage, with the unique advantages of high storage density, fast read/write rate, non-volatility, and no moving parts. Ideally, holographic memory technology may be capable of storing hundreds of billions of bytes of data, transferring them at a rate of a billion or more of bits per second and selecting a randomly chosen data element in 100 microseconds or less.
To date, no state-of-the-art electronic memory technology offers all of the advantages that may be obtained with holographic memory. Dynamic Random Access Memory (DRAM) or Static Random Access Memory (SRAM) are both volatile and require constant refreshing. Electrically Erasable Programmable Read Only Memory (EEPROM) is nonvolatile and has read/write functionality, but it has less storage capacity and a very slow rewrite speed. FLASH memory is nonvolatile and has read/write capability but it too has less storage capacity.
Many devices (e.g., compact discs and digital video discs) use light to store and read data. However, prior art optical storage methods have limited transfer rates and capabilities. To overcome the disadvantages of the prior art, holographic memory may be used. Holographic memory stores information beneath the surface of the recording medium and uses the volume of the recording medium for storage. To date, holographic memory systems have been limited with respect to speed due to the need for re-encoding data and/or reading the data from the storage medium.
Holographic data storage is interesting from a business as well as scientific perspective. At least two companies today claim storage media capable of write once, read many (WORM) for storage markets such as video archival and medical applications. One company, Aprilis, Inc. (a division of STX Group), is producing 120 mm discs for which 400 GB storage capacity and 125 MB/s data transfer rate is claimed to be possible when used in a properly designed disc drive system. A second company, In-Phase Technologies (now controlled by Signal Lake), claims 300 GB and 20 MB/s in the near term with the hope to reach terabyte densities in the future.
While these companies are able to produce storage devices that can store much data, they are not able to achieve the data storage and access speeds needed for a commercially viable product.
Current holographic storage devices are typically record only and have no bulk erase capabilities. Therefore, current art electronic storage devices are slow to erase to a clean state, which, may be needed to meet requirements of some customers.
One way to bulk erase a holographic storage device is to temperature bulk erase. This is accomplished by removing the crystal from MUHCS storage device and placing the crystal in a dielectric holder. It is then inserted into a convection oven and the temperature is set to 200° C. for two hours. While this method may achieve erasure of the photorefractive crystal, it is not a timely or procedurally simple.
Therefore, there is a need in the field to provide bulk erasure in a holographic storage system that is not as time intensive as previous methods and/or procedurally complicated.